This invention relates to a method of preparing metal sulfonates by electrolysis utilizing a membraneless electrolytic cell.
Aqueous solutions of certain metal sulfonates are used, for example, for the electrolytic or currentless deposition of metal or metal alloys, for electrolytic coloring of aluminum and aluminum alloys, and in electrical batteries.
In the electronic industry today, tinning or solder plating is utilized for pre-coating electronic components to enhance their solderability. Aqueous plating baths containing fluoborates have been used widely to permit high-speed uniform metal plating of metals such as tin, lead, or tin-lead alloys. However, the baths containing fluoborates generally are quite corrosive and toxic requiring special equipment which is expensive and presents difficulties in operation including the disposal of the waste water. More recently, the baths containing fluoborates are being replaced by baths containing an alkyl sulfonic acid and a tin alkyl sulfonate, lead, alkyl sulfonate, or mixtures thereof. Thus, there is a need for the effective production of various metal salts of organic sulfonic acids such as methane sulfonate, particularly solutions of metal sulfonates containing from 15 to 30% by weight of the metal sulfonate.
In one embodiment, the invention is a method for preparing a metal sulfonate by electrolysis which comprises:
(A) providing a membraneless electrolytic cell having an upper section and a lower section, and comprising:
(i) an anode comprising at least one metal positioned in the lower section of the electrolytic cell, and
(ii) a cathode positioned in the upper section of the electrolytic cell
(B) charging to the cell, an aqueous solution of an organic sulfonic acid,
(C) passing a current through the cell whereby the metal of the anode dissolves in the sulfonic acid and forms the desired metal sulfonate,
(D) accumulating the metal sulfonate in a lower portion of the lower section of the cell, and
(E) recovering an aqueous solution of the desired metal sulfonate from the lower portion of the lower section of the cell.
A variety of metal salts of various sulfonic acids can be prepared by the method of the invention. In one embodiment, the metals are selected from precious metals, copper, nickel, zinc, lead and tin.